PSIO 201 5th Edition Lecture 19Outline of Last Lecture SarcomereOutline of Current Lecture I. Excitation Contraction CouplingII. TermsIII. ExcitationIV. EC CouplingV. ContractionVI. RelaxationCurrent Lecture- Excitation – electrical signal is transmitted from a motor neuron to the muscle fiber- Excitation- contraction coupling – the events that connect excitation to contraction- Contraction- the events that cause the sarcomere and the muscle fiber to shorten- Relaxation- the events that cause the sarcomere and the muscle fiber to return to resting length.Sequence of events –1. electrical signal transmitted from a motor neuron to a skeletal muscle fiber (excitation)2. triggers release of Ca2+ from SR ( EC coupling)3. Ca2+ brings to troponin on the thin filament, crossbridge forms (contraction)4. Removal of Ca2+ (relaxation)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A) Excitation : Neuromuscular Transmission- Activation of skeletal muscle is voluntary- Requires a signal from the central nervous system- Signal results in electrical impulse Steps of Excitation :1. Action potential arrives at synaptic end bulb of motor neuron and causes opening of voltage gated Ca2+ channels2. Synaptic vessels containing the neurotransmitters, ACh goes under exocytosis3. Ach is released into the synaptic cleft and binds to Ach receptors on the sarcolemma. (motor end plate)4. ACh receptors open and allow Na+ to enter the muscle fibers, generating action potential on sarcolemma.5. ACh is quickly broken down to acetate and AChE B) Contraction Coupling: Release of Ca2+ from SR1. AP runs along sarcolemma, continues into T-tubules2. Triggers release of Ca2+ from SR3. Ca2+ diffuses into sarcoplasm and myofibrils4. Ca2+ bings to Toponin on thin filament5. Crossbridges form and tension is generated ( Contraction)C) Relaxation : Sequestrations of Ca2+1. When AP’s stop arriving at the NMJ, the “trigger” to release Ca2+ from the SR stops2. Active Ca2+ transporters in the SR membrane pump Ca2+ back into the SR3. Cytoplasmic Ca2+ decreases4. Myosin binding sites get covered by tropomyosin 5. Crossbridge cycling stops and tension drops6. Titin brings the sarcomere back to resting
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